Ram type valve assemblies have long been known for effectively sealing off fluid flow through the valve bore. Illustrative of these types of valves, are the ones depicted, for example, in Volume 1, pages 1288-1289, of the "Composite Catalog of Oilfield Equipment and Services", 33rd Revision, 1978-79, published by World Oil. In that the teachings and improvements of the present invention are particularly adaptable to the types of valve apparatus therein depicted and described, such disclosure thereof is accordingly herein incorporated by reference with respect to the overall general construction and operation of such ram-type valve assemblies.
Such valve assemblies are typically provided with two piston-like rams disposed in opposed relation, and means for moving the rams transversely to the valve bore. Upon inward movement of the rams into the bore, sealing engagement is thereby effected between seals carried on the ends of the rams proximal to the bore, thus effectively terminating fluid flow therethrough.
Means for effecting said movement of each of the rams frequently comprises a hydraulically actuated cylinder having a piston interconnected to the respective ram by a shaft or a "stem". The stem is variously provided with stem packings or seals disposed about the stem to prevent pressure and fluid in the valve bore from being communicated along the stem and into the hydraulic circuit of the cylinder. However, not infrequently these seals would fail due to wear, improper seating, excessive borehole pressure, or the like, resulting in contamination of the aforementioned hydraulic circuit with borehole fluid.
Even more serious, however, it was found that such leakage could, in some instances, serve as hydraulic fluid, actuating the cylinders and forcing the pistons thereof radially outward of the bore. This, in turn, would pull the rams apart, thus breaking the aforementioned sealing of the rams, whereby the bore was no longer sealed off, further resulting in loss of control of the flow through the bore and, in some instances, for example, loss of control over the well.
One attempted solution has been to provide secondary manually energized seals which are energized with plastic packing through small check valves. This may be seen on page 1289 of the aforementioned composite catalog and is well known in the art.
Although this attempt to provide redundant sealing along the stem has met with relative success, it was found to be unsatisfactory in some respects for several reasons, only one of which being that the seals will, in time, begin to leak if not properly maintained. Thus, it remained extremely desirable to find a means for completely and reliably isolating the valve bore from the hydraulic circuit of the operating cylinders.
Each ram assembly in the ram-type valve apparatus of the prior art was further typically provided with a pair of pistons rigidly affixed at one end to the valve housing and extending outward in the same general direction as and on either side of a respective ram stem. A conventional bonnet was further provided having two cylinders each disposed about its respective piston, the aforesaid bonnet being rigidly affixed to the valve housing in like manner to the pistons, by means of bonnet bolts. This combination of the bonnet and pistons was interconnected to the hydraulic circuit of the operating cylinder, whereby, upon removal of the bonnet bolts and further charging of an appropriate port of the hydraulic circuit, the bonnet may thereby be made to travel radially inward and outward of the bore in like manner to the operating cylinder. The operating piston was typically retained in the aforementioned operating cylinder which formed a part of the bonnet, and the operating piston was interconnected to the ram by the hereinabove noted stem. It will thus be appreciated that the aforesaid outward movement of the bonnet, which was no longer restrained by the bonnet bolts, would continue further out, thereby pulling the ram along ram guideways outwards of the bore and further than its normal inward and outward operating stroke, so as to render the ram accessable for servicing, such as changing the inner seals, and the like.
However, it will be readily apparent that, in addition to the hereinabove noted sealing problem, yet another drawback of the designs of the prior art was that each ram required three cylinders and pistons. It would thus be highly desirable to reduce the number of cylinders required not only in the moving of the ram assemblies inward and outward of the bore during normal sealing operation, but in the aforementioned hydraulic movement of the ram assemblies further outward of the housing for purposes of servicing the ram assemblies.
The disadvantages of the prior art including those hereinabove recited are overcome by the ram-type valve assembly of the present invention.